The present invention relates to a linear motor for moving an object such as a curtain, having a guide rail for slidably guiding a runner to which the object is connected.
A prior art linear motor is disclosed, for instance, in the Japanese Laid-Open Utility Model No. 60-98489. The linear motor disclosed in this utility model comprises a guide rail and a runner to which one end of an object such as a curtain is fixed. The runner is slidably guided in the guide rail and linearly driven to open and close the curtain.
To drive the runner linearly, permanent magnets are continuously disposed in the guide rail such that adjacent magnets have different polarities. A pair of comb-like electrodes connected to a power source are arranged in the guide rail to extend in the longitudinal direction of the guide rail. The runner is provided with power supplying brushes slidably contacting the comb-like electrodes, and coils energized by the brushes.
When the coils of the runner are energized, the runner is linearly driven by currents flowing in the coils and the magnetic flux of the permanent magnets in the guide rail according to Fleming's left-hand rule. According to the movement of the runner and depending on a contacting state between the comb-like electrodes arranged in the guide rail and the brushes of the runner, the polarities of the coils of the runner are changed such that the runner is linearly driven in the same direction.
In such a prior art linear motor, the runner is energized through the comb-like electrodes provided in the guide rail and the brushes provided in the runner so that the structure of the motor is complicated, and the electrically sliding portions tend to cause imperfect contact, causing a malfunction and deteriorating durability. Further, the runner, due to its structure, requires a separate driving circuit so that the runner and the driving circuit are installed at different locations, causing a problem that operating efficiency in assembly is reduced.
A movable coil-type linear motor in the prior art is disclosed, for instance, in the Japanese Laid-Open Utility Model No. 59-179482. According to the disclosure, permanent magnets are continuously disposed in a band-like shape along a rail such that S-poles and N-poles appear alternately. A pair of the bands of permanent magnets are arranged to face each other such that each pair of permanent magnets which face each other have opposite polarities. Between the bands of permanent magnets, there is movably disposed a runner having coils and current collecting brushes.
The direction of current flowing through the coils must correspond to the polarity of the permanent magnets such that a thrust force is generated by the current flowing through the coils and the magnetic flux of the permanent magnets. To satisfy this requirement, a pair of contact wires cross each other between adjacent different magnetic poles in an extending direction of the permanent magnets, and the collecting brushes of the runner collect electricity from the crossing pair of the contact wires. When the collecting brushes are moved, sparks are caused by electrical gaps at the crossing portions of the contact wires. Due to the sparks, the collecting brushes tend to be worn, rapidly deteriorating the durability thereof and destabilizing the supply of power to the coils.